It is well known that certain electronic products, such as computers, are sources of electromagnetic interference (EMI) and radio frequency interference (RFI). This troublesome interference can disturb the operation of nearby electronic equipment such as radios, televisions and sensitive analog circuitry. As a result, there are strict federal and international standards imposed on the amount of conducted and radiated EMI and RFI that is permitted in commercial products. There is therefore a need to provide enclosures for electronics products that prevent EMI and RFI from being conducted or radiated outside of the enclosure.
It has been found that no matter how mechanically tight a joint is made between two surfaces of an enclosure, EMI and RFI can take place unless there is electrical continuity between the two surfaces. In order to provide the required electrical continuity in the joint, conductive elastomer gaskets, flexible metal strips and the like are frequently used. The gaskets or strips are sandwiched between the two surfaces and provide electrical continuity between the surfaces of the enclosure. A Faraday cage surrounding the electronics product is thereby formed by the enclosure, preventing EMI and RFI outside of the enclosure.
When installed properly, elastomer gaskets and the like perform well and satisfy stringent military requirements. A problem with these gaskets, however, is that they cause the force needed to assemble the enclosure, (the closure force), to be relatively very high. This high closure force necessitates the use of a relatively large number of fasteners to hold the two surfaces of the joint together. The assembly cost and time needed to enclose a product increases greatly with the use of a large number of mechanical fasteners. Furthermore, the cost of these gaskets themselves is relatively very high.
The high closure force of the conductive elastomer gaskets and the like also makes these gaskets unsuitable for use with creep-prone materials, such as plastic. Instead, they are better suited for use with metal enclosures. With certain plastic materials, however, which are now being used for computer enclosures more frequently, the surfaces tend to move and thus in time to creep apart when a force is applied against the surface of the plastic. Electrical continuity in time can therefore no longer be assured between the surfaces of certain plastic enclosures.
A need exists for an arrangement to provide an EMI and RFI-tight joint between surfaces of an enclosure that requires a relatively low closure force. This would allow the enclosure to be made of plastic and other creep-prone materials and reduce the assembly costs of the enclosure.